Characterization of surface markers on B cells at successive stages along the differential pathway from early precursor to antibody forming cells (AFC) a) H chain class and allotypes of surface immunoglobulins (Ig): relationship to Ig produced by progeny AFC; ontogeny; functional role; b) VH markers: relationship to Ig produced by Progeny AFC; genetic control; c) Non-Ig surface markers: Correlation with H chain class; ontogeny; genetic control; functional role with respect to Ab production; Isolation and characterization of subsets of T or B cells and definition of their function(s) in humoral immunity. Development and study of Ig allotype (CH) congenic strains; a) New congenic strain development; maintenance and genetic testing of existing congenic strains; b) Study of Ig regulatory abnormalities in congenic strains. Production and characterization of monoclonal (hybridoma) Ab for use in above studies; a) Monoclonal Ab specific for Ig isotype (class), allotype or idiotype; b) Monoclonal Ab specific for non-Ig determinants on B cells; c) Monoclonal Ig (specificity irrelevant) carrying allotypic and idiotypic determinants not carried on known myeloma proteins.